1. Field of the Invention
This invention relates to an apparatus for making a non-woven fabric, comprising carding drums, which are provided with teeth and rotate in the same sense and closely succeed each other in the direction of travel of a preliminary web, wherein each of said carding drums which succeeds another in the direction of travel of the preliminary web cooperates as a worker roller with the preceding carding drum, discharge ducts are provided, which extend into respective generally triangular spaces between adjacent carding drums and at least adjacent to one of their two boundary walls extending in the longitudinal direction of the adjacent drums are formed with at least one air inlet opening, which extends over the length of said wall, and a continuously moved, air-permeable collecting surface is provided, to which suction is applied adjacent to each discharge duct and which serves to collect those fibers of the preliminary web which have been thrown off from the carding drums under the action of centrifugal force.
2. Description of the Prior Art
Apparatuses of that kind are known from Austrian Patent Specification No. 348,830. In said apparatuses, the carding drums are arranged in close succession, each succeeding carding drum can comb out like a worker roller fibrous material from the preceding carding drum and those fibers which have not been combed out will be thrown off onto the collecting surface immediately after the combing operation. This will result in an excellent disintegration of the preliminary web and it is possible to divide the preliminary web in a simple manner into a plurality of partial streams of fibers because each succeeding carding drum performs an additional combing operation, which provides fibrous material for at least one additional partial stream. As a result, the partial stream of fibers flying from each carding drum may have a low fiber density even though the throughput rate of material moving through the apparatus is comparatively high. In combination with an application of fibers in a plurality of layers, that low fiber density is a requirement for the making of a non-woven fabric which is highly uniform. But such a highly uniform non-woven fabric cannot be achieved unless an undisturbed and uniform deposition of the fibers on the collecting surface is ensured. To provide a suitable air flow for entraining the fibers, air inlet openings are required at the discharge ducts. It has been found, however, that such air inlet openings are less desirable than blast nozzles, which are provided on that side of the carding drums which is opposite to the collecting surface, as is proposed in Austrian Patent Specification No. 379,619 and the corresponding U.S. Pat. No. 4,534,086. This is so because the air which is discharged by said blast nozzles flows through the throats between adjacent carding drums and can be controlled to ensure that the air streams in the discharge ducts will match the velocity at which the fibers are thrown off and said air will assist the separation of the fibers from the carding drums. But as the working width increases, the diameters of the carding drums and, as a result, the flight distances of said fibers, are increased and the increasing flight distance of the fibers will promote an agglomeration of fibers. For this reason, larger working widths will adversely affect the uniform delivery of fibers to the collecting surface, particularly adjacent to those boundary walls of the discharge ducts which extend along the carding drums. Such disturbances must particularly be expected because an electrostatic charging of the fibers adjacent to said boundary walls may cause the fibers to deposit on the boundary walls.